1. Field of the Invention
The present invention relates to the field of ultraviolet detection, and in particular to an organic p-n junction based ultraviolet detection device and an ultraviolet image detector using the device.
2. the Related Arts
Ultraviolet detection has been widely used in various applications, such as flame detection and combustion control, solar radiation detection, ultraviolet source control for water treatment and surface disinfection, ultraviolet purification, ultraviolet disinfection, food sterilization control, splitter, and arc detection.
For ultraviolet light of 0.185-0.260 nm wavelength generated by burning flame, a sensitive element that is made of a solid-state substance, such as silicon carbide (SiC) or aluminum nitride (Al(NO3)3), can be used for detection of the ultraviolet light. Based on the type of explosion protection, the sensitive element is classified as explosion-proof type and stable type. These sensitive elements can be used in the following applications: (1) exploration, production, storage, and unloading of mineral oil and natural gas; (2) manufacture of automobiles and aircrafts and paint spraying chambers; (3) explosives and military supplies; (4) medicines; (5) scrap incineration; and (6) production, storage, and transportation of high-risk industry dyes, such as powder compartment.
Ultraviolet light also has wide applications in medicine and biology and is particularly of unique use in diagnosis of skin diseases recently. The application of ultraviolet detection in diagnosis of skin diseases allows for direct observation of details of lesions and also enables inspection of cancel cells, microorganisms, hemachrome, red blood cells, white blood cells, and cell nuclei. Such detection is not just efficient and precise, it is also direct and clear.
There are also military applications, such as ultraviolet guidance. Although infrared guidance is the main stream guidance of guided missiles, with the maturation of infrared defense technology, the offensive effect achieved with infrared-guided missile will be severely affected. To compete with infrared defense technology, guidance techniques have been developed in a direction toward dual-color guidance, which includes infrared-ultraviolet guidance. When being subjected to infrared interference, a missile can still be guided by ultraviolet radiation that emits from an ultraviolet detector to detect a target toward the target for attack.
For communication, ultraviolet communication, which is a novel way of communication showing great potential for future development, uses ultraviolet radiation to transmit messages and, compared to the regular radio communication, possess advantages of low eavesdropping rate and high interference resistance and enable achievement of near distance secure communication, and, compared to the advance laser communication, possesses advantages of omnidirectional multi-channel communication and oriented communication.
Further, fingerprints and body fluids (such as blood, sperm, and saliva) and substances, such as contraband gunpowder and narcotics show unique characteristics of absorption, reflection, diffraction, and fluorescence. Ultraviolet imaging techniques for police applications use the characteristics of such substances with respect to ultraviolet light to magnify and convert an ultraviolet image taken with an ultraviolet imaging device into a visible light image in order to uncover messages hidden therein, allowing criminal investigation personnel to easily and immediately read for identifying important evidences and also for retrieving evidence through photographing. Digitalized photographing and real-time search of criminals through computer networks allows for greatly shortening of case handling time and enhancing operation efficiency. Compared to the traditional scene investigation for trace searching and retrieval, the ultraviolet imaging systems for police applications, if used for the same jobs, has a primary advantage of enabling fast observation, searching, positioning, evidence-obtaining, and photographing without additional processing. This greatly improves the operation efficiency and also, due to realization of fast and direct searching, allows for identification of some traces and evidences that cannot be identified with the traditional ways. Further, such a method requires no direct contact with evidences and thus greatly improves the retrieval and utilization rate of evidence. All these advantages makes it well appraised in the field of criminal investigation.
Ultraviolet light is divided into middle ultraviolet in the wave range of 0.2-0.3 μm and near ultraviolet in the wave range of 0.3-0.4 nm. The middle ultraviolet light contained in sun light is almost absorbed by the ozone layer of the atmosphere and thus, this wave range of ultraviolet light is often referred to as “solar blind range”. Ultraviolet detection technology uses this wave range of the middle ultraviolet light.
Ultraviolet spectrum imaging inspection technology is a novel inspection imaging technique developed in the European and American countries for military purposes. The characteristics of this technique is observing and inspecting ultraviolet signals in the “solar blind range” (240-280 nm) and converting the ultraviolet image signals into visible light image signals for inspection and survey. Using the technology allows for various physical, chemical, and biological phenomena that cannot be detected with the traditional optic instrument. Further, since it operates in the wave range of the “solar blind range”, it is not interfered with by sunlight. In other words, instrument employing such technology is operable in sunlight to provide clear images and is reliable and easy to use. There has already been instrument of this kind put into practical use in European and American developed countries and Russia. The instrument of this kind is applicable to the fields of electrical system inspection, space science, and environmental protection researches.
An inorganic ultraviolet imaging inspection system generally comprises: an ultraviolet imaging object lens, an ultraviolet filter, an ultraviolet image enhancing system, a charge coupled device (CCD), and an image displaying system. The principle of operation is illustrated in FIG. 1, in which an ultraviolet signal source 100 is irradiated by background light (including visible lights, ultraviolet light, and infrared light) and what is transmitted from the ultraviolet signal source 100 to an ultraviolet imaging lens 200 includes the ultraviolet light radiating from the ultraviolet signal source 100 itself and components of the background light reflected by the ultraviolet signal source 100. An imaging ray, after passing through the ultraviolet imaging lens 200, is subjected to filtering of a portion of the background light, with a portion of the background lighting still remaining. The ray is then transmitted through an ultraviolet filter 300, which allows for passage of light of the “solar blind range” only, to irradiate a photoelectrical cathode of an ultraviolet image enhancing device 400. Through the enhancement realized with the ultraviolet image enhancing device 400, the ultraviolet signal is enhanced and amplified and converted into and output as a visible light signal. Afterwards, the imaging ray passes through a CCD camera 500 and is finally subjected to signal processing and supplied to a displaying device 600 for observation and recording.
The materials that are used to make inorganic ultraviolet detectors include: first-generation elemental semiconductor materials, second-generation compound semiconductor materials, and third-generation wide band gap semiconductor materials. The first-generation elemental semiconductor materials primarily include silicon (Si); the second-generation compound semiconductor materials primarily include gallium arsenide (GaAs) and indium phosphide (InP); and the third-generation wide band gap semiconductor materials primarily include silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), and diamond. Due to certain features, including small forbidden band width, large cutoff wave length for long waves of device, and low maximum operation temperature, the first-generation semiconductor materials and the second-generation compound semiconductor materials impose heavy limitations to the characteristics and use of the ultraviolet detectors, making it not meeting the needs for practical applications. The third-generation wide band gap semiconductor materials have various characteristics, including large forbidden band width, high electron drafting saturation speed, small dielectric constant, and excellent thermal conductivity, making they perfectly suitable for electronic devices of radiation resistance, high frequency, large power, and high density integration. The unique forbidden bandwidth also allows them to be used to make light emitters or photo detection device of blue and green lights and ultraviolet light.
Even so, the inorganic ultraviolet detection devices still suffer certain problems, such as high manufacturing cost, complicated operation, high material cost, and incapability of forming thin films on flexible plastic substrates.